-Bprefix option should be passed through GccToolChain::createBuiltInHeaderPathsRunner

When calling a cross-toolchain, certain flags (including --sysroot) are passed through from the

ProjectExplorer.GccToolChain.PlatformCodeGenFlags to the code model's probing.

https://github.com/qt-creator/qt-creator/blob/4032f6383a411768ddf6e6059aaed6c552fb65da/src/plugins/projectexplorer/gcctoolchain.cpp#L564-L570

For the winegcc wrapper (and probably others?) to work with a cross-toolchain not normally in $PATH, -Bprefix is also needed, and feels appropriate alongside --sysroot (one is where to find host executables, the other where to find target libraries and headers). https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html#Directory-Options

Could that be added?